Opt-In Downloads (formerly Subscribe & Download) is a plugin that allows to distribute files through subscriptions. If people want to download something from your website or from third party websites they must submit their contact details. After submission they receive download link by e-mail. Very simple workflow.
All submitted data is saved in database and/or can be sent to popular email marketing providers such as MailChimp, iContact, GetResponse, etc. All saved data can be exported as CSV-file to be used with any other newsletter systems. Opt-In Downloads is a perfect way to extend functionality of your website.